A study on stainless steel mirror surface polishing by using the electrophoretic deposition method

Polishing wheels with homogeneously organized micro abrasive grains, uniformly dispersed by electrophoretic deposition (EPD), can be applied in mirror-like polishing process. This work studies the characteristics of EPD and mechanical polishing when SUS316LVV is polished. Abrasive grains with blunt edges are easily ablated from the polishing wheel by friction during polishing. The polishing wheel can be continuously refreshed by adding new abrasives. A superior surface polishing quality can thus be obtained. The control parameters of the EPD polishing process include the working voltage, the rate of rotation of the polishing wheel, the polishing feed rate, the polishing time, the axial loading and the pH value of the electrolyte, etc. Experimental results indicate not only that SiC particles of size 0.9–1.5 μm were used in EPD polishing, but also that the initial roughness of a machined surface could be improved from 0.5 μm Ra to 0.02 μm in 8 min, yielding a mirror-like surface.     

In-situ laser-fabrication and characterization of TiC-containing Ti–Co composite on pure Ti substrate

This work presents the in-situ fabrication of a layered metal-matrix composite coating on a pure Ti substrate. The coating consists of a matrix of cobalt-titanium intermetallics and the reinforcement phase of titanium carbide. The fabrication process is laser cladding, conducted using a pre-placed powder mixture of elemental titanium, cobalt, and graphite. Several materials characterization methods including microscopy, microhardness and nano-indentation are used to study the coating and coating–substrate interface. The intermetallic phases in the matrix vary from Co-rich phases at the coating surface to Ti-rich compounds near the substrate. The interface is revealed to have a smooth profile, free of any porosity or cracks, with good metallurgical bonding to the substrate. A relatively uniform hardness in the range of 1200–1300 HVN is achieved through a depth of 200 μm into the coating. The hardness then gradually decreases to 480 HVN at the substrate interface, approximately 300 μm from the surface. The hardness evolution, which is predictable using the Rule of Mixtures, is explained by the fraction of the carbide particles and the type of intermetallic compounds in the matrix.     

Kinetics and formation mechanism of amorphous Fe52Nb48 alloy powder fabricated by mechanical alloying

A single phase amorphous Fe₅₂Nb₄₈ alloy has been synthesized through a solid state interdiffusion of pure polycrystalline Fe and Nb powders at room temperature, using a high-energy ball-milling technique. The mechanisms of metallic glass formation and competing crystallization processes in the mechanically deformed composite powders have been investigated by means of X-ray diffraction, Mössbauer spectroscopy, differential thermal analysis, scanning electron microscopy and transmission electron microscopy. The numerous intimate layered composite particles of the diffusion couples that formed during the first and intermediate stages of milling time (0–56 ks), are intermixed to form amorphous phase(s) upon heating to about 625 K by so-called thermally assisted solid state amorphization, TASSA. The amorphization heat of formation for binary system via the TASSA, ΔH_a, was measured directly as a function of the milling time. Comparable with the TASSA, homogeneous amorphous alloys were fabricated directly without heating the composite multilayered particles upon milling these particles for longer milling time (86 ks–144 ks). The amorphization reaction here is attributed to the mechanical driven solid state amorphization. This single amorphous phase transforms into an order phase (μ phase) upon heating at 1088 K (crystallization temperature, T_x) with enthalpy change of crystallization, ΔH_x, of −8.3 kJ mol⁻¹.     

Preparation and electrochemical characterization of porous SWNT–PPy nanocomposite sheets for supercapacitor applications

Highly porous sheets comprised of single walled carbon nanotubes and doped polypyrrole (SWNT–PPy) were prepared by vacuum filtration of SWNT–PPy methanol dispersions. The employed preparation procedure is an extension of conventional bucky-paper fabrication technique for the multi-component system. A number of nanocomposites with nominal SWNT:PPy compositions ranging from 1:0 to 1:1 were obtained and tested. Electrochemical properties of the nanocomposites were investigated by cyclic voltammetry and galvanostatic spectroscopy technique in aqueous 1 M NaCl electrolyte. The highest specific capacitance of 131 F/g was obtained for nanocomposite with 1:1 SWNT:PPy ratio. Prospective applications of prepared materials range from supercapacitors to electrodes for batteries and electromechanical actuators.     

Electrical d.c. conduction mechanism in some newly synthesized mono- and dipyridine quaternary salts in thin films

The study of temperature dependence of the electrical conductivity and thermoelectric power, for some recently synthesized quaternary salts of bipyridine and indolisine pyridine, is reported. Thin film samples (d = 0.10–0.60 μm) deposited from dimethylformamide solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 290–500 K.The studied organic salts behave as typical p-type semiconductors. The activation energy of electrical conduction laid in the range 1.40–1.75 eV, while the ratio of charge carrier mobilities ranged between 0.77 and 0.93.The correlations between determined semiconducting parameters and specific molecular structure of the compounds have been discussed.In the higher temperature range (360–500 K), the electronic transport in examined compounds can be interpreted in terms of band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model may be conveniently used.     

The origin of non-uniform microstructure and its effects on the mechanical properties of a friction stir processed Al–Mg alloy

The microstructure of the stirred zone (SZ) resulting from friction stir processing or welding (FSP/FSW) has usually been assumed to be uniform when discussing the mechanical properties. However, numerous works have indicated that the fine-grained microstructures in the SZ were non-uniform, with precipitate, texture and grain size gradients caused by the severe plastic deformation and heat distribution. In this work commercial aluminum alloy 5083-H112 was subjected to FSP and fine-grained microstructures with an average grain sizes of 2.7–13.4 μm were obtained by controlling the FSP conditions. The stress–strain curves exhibited stepped yield point elongation, which was suggested to be associated with these characteristic non-uniform microstructures. Tensile tests indicated that the Hall–Petch relationship held in this FSP alloy when taking account of the average grain size. Toughness analysis indicated that the optimum toughness was anticipated to be obtained around a grain size of 1 μm for this FSP alloy.     

Straightening of micro wires using the direct wire heating and pulling method

In this study, we have developed a novel micro wire straightener using the direct wire heating and pulling (DWHP) method. The straightener can remove the bend of the micro wire (< 200 μm) by heating it with the direct current, which flows through the wire in the glass chamber and simultaneously giving it the appropriate tension. A tension meter was attached to control the tension of the micro wire (tungsten). In order to avoid surface oxidization of the wire, we supplied inert gas (argon) into the glass chamber during the heating process, and examined the effect of the gas flow rate. The effects of the tension and the current applied to the micro wires (tungsten) were investigated experimentally. With Results from various experiments and parametric studies, we could obtain desired straightness (≈1 μm/1000 μm) with a tension of 500–600 gf and an approximate electric current of 1.5 A.     

Si-modified aluminide coatings deposited on Ti46Al7Nb alloy by slurry method

Ti46Al7Nb alloy has been used as the research substrate material for the deposition of water-based slurries containing Al and Si powders. The diffusion treatment has been carried out at 950 °C for 4 h in Ar atmosphere. The structure of the silicon-modified aluminide coatings 40 μm thick is as follows: (a) an outer zone consisting of TiAl₃ phase and titanium silicides formed on the matrix grain boundaries composed of TiAl₃–type Ti₅Si₃; (b) a middle zone containing the same phase components with the matrix TiAl₃ and the silicides Ti₅Si₃, which formed columnar grains; (c) an inner zone, 2 μm thick, consisting of TiAl₂ phase. Cyclic oxidation tests were conducted in 30 cycles (690 h at high temperature) and showed a remarkably higher oxidation resistance of the Ti46Al7Nb alloy with the protective coating in comparison with the uncoated sample.     

In situ nanocrystalline Fe–Si coating by mechanical alloying

A new approach for deposition of in situ nanocrystalline Fe–Si alloy coating on mild steel substrate by mechanical milling has been proposed. The thickness of nanocrystalline coating was a function of milling time and speed. Milling speed of 200 rpm was the optimum condition for development of uniform, hard, adherent and dense 200–300 μm thick nanocrystalline coating. A possible mechanism, consisting of three steps like repeated impact, cold welding and delamination, has been proposed for the formation of coating. These coatings have resulted in the increase of the hardness to almost double the value before coating.     

Determination of the elastic properties of some coated materials by simulation of the analogue signal of the reflection acoustic microscope

We discuss in this work the elastic properties of monolayer materials (layer/substrate). We consider both cases of quick/slow and slow/quick systems. We calculate Young's modulus, shear modulus and Poisson's ratio of the following four systems: Cr/Fe, TiN/Fe, Al/Si and Al/SiC. We make it evident that the use of the simulated acoustic signal of the reflection acoustic microscope yields to the determination of the wave propagation velocity of different modes in the layer/substrate according to the frequency and the thickness of the layer. We demonstrate that Victorov relation is not applicable in this case. A new method, that we called ‘method of homogenization’ is proposed to resolve the problem of dispersion.For the considered materials, the calculations have been carried out in a large range of frequencies (50 MHz–3.5 GHz) and coating layer thickness (0.5–150 μm). We show that for the studied materials the elastic constants take the values of the material layer beyond a thickness of 30–40 μm.     

Ultra-precision surface finish of the hardened stainless mold steel using vibration-assisted ball polishing process

A vibration-assisted spherical polishing system driven by a piezoelectric actuator has been newly developed on a machining center to improve the burnished surface roughness of hardened STAVAX plastic mold stainless steel and to reduce the volumetric wear of the polishing ball. The optimal plane surface ball burnishing and vibration-assisted spherical polishing parameters of the specimens have been determined after conducting the Taguchi's L₉ and L₁₈ matrix experiments, respectively. The surface roughness R_a=0.10 μm, on average, of the burnished specimens can be improved to R_a=0.036 μm (R_max=0.380 μm) using the optimal plane surface vibration-assisted spherical polishing process. The improvement of volumetric wear of the polishing ball was about 72% using the vibration-assisted polishing process compared with the non-vibrated polishing process. A simplified kinetic model of the vibration-assisted spherical polishing system for the burnished surface profile was also derived in this study. Applying the optimal plane surface ball burnishing and vibrated spherical polishing parameters sequentially to a fine-milled freeform surface carrier of an F-theta scan lens, the surface roughness of R_a=0.045 μm (R_y=0.65 μm), on average, within the measuring range of 149 μm×112 μm on the freeform surface, was obtainable.     

Preparation of thin film YSZ electrolyte by using electrostatic spray deposition

Yttria-stabilized zirconia (YSZ) thin film was successfully deposited onto Ni–YSZ anode disk by the electrostatic spray deposition (ESD) technique. To deposit a dense YSZ thin film onto porous Ni–YSZ substrate, the influence of process parameter variables were examined. The relationship between process parameters and morphologies of YSZ films coated by ESD was investigated by means of SEM photography and X-ray diffraction (XRD). The result showed that dense YSZ film of average 10–15 μm thickness was deposited on the porous Ni–YSZ substrate with temperature of 400 °C, the precursor solution concentration of 0.05 M, nozzle-to-substrate distance of 30 mm, applied electric field of 18 kV, and deposition time of 90 min.     

An amperometric enzyme biosensor based on in situ electrosynthesized core–shell nanoparticles

This work describes a new approach to the construction of an amperometric biosensor for hydrogen peroxide detection based on in situ electrosynthesized gold/polyaniline core–shell nanocomposites on conducting ITO electrode. The immobilization of the enzyme, horseradish peroxidase (HRP), on the polyaniline nanofilm was carried out by electrostatic attachment approach. Results showed that the immobilized HRP exhibited enhanced performance toward the reduction of H₂O₂, in comparison with other bulk polyaniline (PANI)-based H₂O₂ biosensor and metallic nanoparticles incorporated PANI systems. The resulting biosensor shows a fast amperometric response (<2 s) to H₂O₂. A linear range from 0.2 to 80 μM for the detection of H₂O₂ was observed with a sensitivity of 20.5 μA/mM and a detection limit of 0.16 μM at a signal-to-noise ratio of 3. Moreover, the biosensor has a good reproducibility, and long-term stability.     

Grain refinement of cast titanium alloys via trace boron addition

The grain size of as-cast Ti–6Al–4V is reduced by about an order of magnitude from 1700 to 200 μm with an addition of 0.1 wt.% boron. A much weaker dependence of reduction in grain size is obtained for boron additions from >0.1% to 1.0%. Similar trends were observed in boron-modified as-cast Ti–6Al–2Sn–4Zr–2Mo–0.1Si.     

A novel white afterglow phosphorescent phosphor Ca3SnSi2O9: Dy

AZ91 alloy powder with 2 mass% Si addition (flakes) was obtained by two-roller quenching equipment with an atomized accessory. The powders were consolidated and extruded into bar. The microstructures of the powders (flakes) and bars were characterized by optical microscope (OM), XRD, TEM and SEM. The results showed that the grain size of the powder were dendritic with the sizes of about 1–5 μm. The as-extruded alloy bars retain equiaxed grains with a large number of precipitated phases, i.e. Mg₂Si, β-Al₁₂Mg₁₇ and AlMg₂Zn. The alloy exhibits excellent mechanical properties. The 0.2% yield tensile strength, ultimate tensile strength and elongation of rupture were 322.47, 429.78 MPa and 6.4%, respectively. The as-extruded alloy bars show preferable elevated temperature mechanical properties.     

Comparative studies of spectroscopic properties in Er–Yb codoped phosphate glasses

A spectroscopic investigation of an extensive series of commercially available Er³⁺–Yb³⁺ codoped phosphate glasses (IOG-1) with different Er–Yb concentrations have been presented based upon spectroscopic measurements and Judd–Ofelt theory. The composition and the atomic concentration of the respective elements of the glass samples were analyzed. Various spectroscopic parameters were obtained to evaluate the performances of these glasses as a laser material in the eye-safe laser wavelength of 1.53 μm. Using the measured fluorescence lifetimes the radiative quantum efficiency of the ⁴I_13/2 → ⁴I_15/2 transition is estimated to be 100% for the glass substrates with an Er³⁺ concentration of lower than 2.0 × 10²⁰ ions/cm³. The stimulated emission and absorption cross-sections were also determined and compared. The infrared and upconversion fluorescence were studied, and under 975 nm excitation the dominant upconversion mechanisms are excited state absorption (ESA) and energy transfer (ET) for the green emission, and ET for the red emission. The data obtained here provide useful guidelines on the choice of IOG-1 glasses with the fixed Er–Yb concentrations.     

Application of micro-EDM combined with high-frequency dither grinding to micro-hole machining

This research presents a novel process using micro electro-discharge machining (micro-EDM) combined with high-frequency dither grinding (HFDG) to improve the surface roughness of micro-holes. Micro-EDM is a well-established machining option for manufacturing geometrically complex small parts (diameter under 100 μm) of hard or super-tough materials. However, micro-EDM causes the recast layer formed on the machined surface to become covered with discharge craters and micro-cracks, resulting in poor surface quality. This affects the diameter of the micro-hole machined and undermines seriously the precision of the geometric shape. The proposed method that combines micro-EDM process with HFDG is applied to machining high-nickel alloy. As observed in SEM photographs and surface roughness measurement, HFDG method can reduce surface roughness from 2.12 to 0.85 μm Rmax with micro-cracks eliminated. Our results demonstrated that micro-holes fabricated by micro-EDM at peak current 500 mA followed by HFDG at 40 V can achieve precise shape and good surface quality after 6–8 min of lapping.     

Experimental investigation of the effect of solidification processing parameters on the rod spacings in the Sn–1.2 wt.% Cu alloy

Sn–1.2 wt.% Cu alloy was prepared in a graphite crucible under the vacuum atmosphere. The samples were directionally solidified upwards under argon atmosphere with different temperature gradients (G = 2.69–8.88 K/mm) at a constant growth rate (V = 6.80 μm/s) and with different growth rates (V = 2.78–136.36 μm/s) at a constant temperature gradient (G = 2.69 K/mm) by using a Bridgman-type directional solidification apparatus. The microstructure of Sn–1.2 wt.% Cu alloy seems to be rod eutectic structure. The rod spacings (λ) were measured from both transverse and longitudinal sections of the samples. The influence of the growth rate (V) and temperature gradient (G) on the rod spacings (λ) and undercoolings (ΔT) was analysed. The values of λ²V, λ²G, ΔTλ, ΔTV^−0.5 and ΔTG^0.5 were determined by using the Jackson–Hunt eutectic theory. The results obtained in the present work have been compared with the similar experimental results obtained in the previous works for binary alloys.     

Accurate tracking controller design for high-speed drives

This paper presents a motion control strategy that utilizes a combination of vibration avoidance, sliding mode control, and torque ripple and friction compensation techniques to facilitate high bandwidth–high accuracy tracking in ball screw drives. Torsional vibrations are modeled with finite element analysis and experimentally identified. Excitation of the first and second mode is avoided by designing appropriate notch filters. Following the attenuation of structural vibrations, rigid body motion is controlled using adaptive sliding mode control, where a positioning bandwidth of 223 Hz is achieved. Nonlinear friction and motor/mechanical torque ripples are modeled and compensated in feedforward. With the proposed control strategy, an experimental tracking accuracy of 0.95 μm has been achieved while traversing the axis at a feedrate of 1000 mm/s with 1g acceleration.     

Tribology of thermal sprayed WC–Co coatings

This paper looks at the tribology of thermal sprayed WC–Co based coatings and covers the high energy air–sand erosion resistance and slurry jet impingement erosion performance, dry and wet sliding tribology of thermal spray WC–Co based coatings as well as the abrasion and abrasion–corrosion of these coatings. The tribological and tribo-corrosion performance of the coatings will be related to their mechanical and corrosion properties as well as deposition parameters, microstructure and actual composition. For example, the anisotropic microstructure of thermally sprayed WC–Co–Cr coatings, in particular the low fracture toughness in a direction parallel to the substrate, has been observed to affect the nature of crack formation under 200 μJ air–solid particle erosion conditions. Voids and occasionally other microstructural features (i.e., cobalt lakes, splat boundaries, interfacial inclusions) in the coating act as crack initiation sites. The erosion rate was dominated by cracks within 5 μm of the surface and was relatively insensitive to total length of cracks, showing a near-surface damage front controls the erosion rate and this region is coincident with the region of maximum shear stress induced by erodent impacts. Optimisation of the deposition parameters of HVOF 86WC–10Co–4Cr coatings show an improvement in erosion resistance of more than 50% over the conventional D-gun applied coating of identical nominal composition. The variation in the slurry erosion performance of the thermally sprayed coatings is also linked to directional fracture toughness and crack propagation paths which are influenced by the presence of pores, inhomogeneous carbide distributions and substrate grit blast remnants. The influence of slurry jet angle is more pronounced under 0.4 μJ energy conditions where maximum erosion occurred at 90° and the minimum at 30° in contrast to 7 μJ slurry erosion rates which were independent of jet angle. This reflects the lower levels of fluctuating stresses imparted to the coating during low energy slurry impacts leading to the impact angle having a greater effect on sub critical crack growth rate than for higher energy conditions.The abrasion resistance of these coatings was found comparable to sintered cermets of the same composition. The synergistic effects between micro and macro abrasion and corrosion for detonation gun (D-gun) sprayed WC–10Co–4Cr coatings are shown to be significant and depend on the environment. The size effect of the abradant relative to the microstructure and splat size is important as well as the propensity for the various phases to passivate to control corrosion levels. Comparisons between exposed and freshly polished coating surfaces in strong NaOH solutions (pH 11) show that significantly lower wear rates were seen for the exposed surface due to a negative wear–corrosion synergy due to selective phase removal and the effects of localised passivation.Dry and wet sliding wear resistance of these coatings is shown to be high (wear rates of 10⁻¹⁶–10⁻¹⁸ m³/Nm) with modest coefficient of friction levels between 0.2 and 0.5. The presence of oxides on the binder phases appears to influence the friction and wear levels. Wear appears to be by carbide ejection and/or by tribo-chemical processes.